The conventional open wrench generally includes a driving head connected to the handle and the driving head has a clamping opening so as to be mounted to the head of a bolt. In order to increase the durability of the driving head and reduces the material and weight, there are two recesses located at the bottom of the two clamping arms of the driving head. Although the open wrench has the two recesses defined in the bottom of the two clamping arms, the strength of the wrench is still not satisfied.
The present invention intends to provide an open wrench which has lightweight and the material required is less than the conventional wrenches.